I'm running Vittoria cyclocross tires on my commuter. They're 30c I think...pretty skinny. There are a lot of 700c options out there. I had 35c schwalbe kojacks for a while, and I really liked them. They're basically a slick.
(other tires I'm running are apparently old cause I can't find them anymore on kenda or continental's websites!)
edit: sorry, I'm talking winter snow riding here... the marathon's will still be fun in summer.
I also suggest specialized armadillos, they're really tough, not terribly sticky unfortunately, but they last a good while.
Or if its road only riding why not get some road tires, like 28 or 30c. For group road rides I have a spare set of road wheels and tires ready to go. With same cassette (luckly I run a road cassette on my CX when riding it off road.) That could be an option too. Just takes a quick brake cable adjust.
If you want one tire to cover all your needs, I've found Crossmarks to be nice rolling tires that handle dirt well. If you're not pushing into 20mph+ speeds, I don't think you lose too much by having fatties. If you're on road with lots of debris, you probably want something with an armored casing (or go tubeless).
If you're basically using a 29er to commute, these should be fantastic. I haven't ridden them, but I saw a bike locked up outside a bar that had these. They're huge and probably heavy, but they should deal with public pavement very nicely.
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